In the prior art, it is known to produce preparations by mixing substances in a vat and introducing powdered particles into said vat so as to incorporate them into the mixture.
Such preparations are for example commonly manufactured for pharmaceutical, cosmetic, agri-food and other applications. For pharmaceutical or cosmetic applications in particular, the incorporated particles may make up the active ingredient of the composition and must then be incorporated into the mixture in very precise proportions. The final mixture must furthermore be as homogenous as possible.
In order to produce such preparations, mixing assemblies are known. According to the most widespread technology, these comprise a vat, wherein an under-pressure is maintained and which is designed to receive the mixture, a rotor including mixing blades and cooperating with motor means so as to be rotated, and a stator including an annular ring surrounding the rotor and having radial openings for the passage of the mixture projected radially by said rotor.
Two methods are commonly used to incorporate particles into the preparation.
According to a first method, the particles are introduced by suction into the vat, in which an under-pressure is maintained, by means of a conveying line emerging in the bottom of the vat, laterally with respect to the rotor-stator unit. The conveying line is equipped with a valve making it possible to command the introduction of particles into the vat. The particles to be incorporated into the mixture circulate in the vat approximately following a convection path of the mixture in the vat. However, in this case, the introduction flow rate of the powder is directly related to the vacuum level in the vat. Consequently, for a given valve, the vacuum must be increased to increase the flow rate of introduced particles. However, depending on the viscosity of the mixture in the vat, an excessively high vacuum level creates too fast a passage of the particles through the mixture and the aspirated particles become glued against the upper part of the vat; this generates cleaning and product loss problems. This is particularly significant when the injected product is the active ingredient of the final mixture, which may then be under-dosed.
According to a second method, the mixing assembly is equipped with an outside pipe allowing recirculation of the preparation. In this embodiment, the powdered particles are introduced into the vat by means of a conveying line emerging in the outer pipe forming a recirculation loop. However, this method poses cleaning problems for said outside pipe. Furthermore, the introduction flow rate of the powder is limited by the dimensions of the outer pipe and the circulation flow rate therein.
In order to offset these drawbacks, the applicant has developed a third method making it possible to effectively disperse particles in a mixture with a high flow rate and reducing product losses. This method is described in document FR 2,929,133.
According to this method, the particles are introduced by suction into the vat kept, in which an under-pressure is maintained, by means of a conveying line emerging in the vat at the rotor of the rotor-stator unit. The conveying line is equipped with a valve making it possible to command the introduction of particles into the vat. The particles to be incorporated into the mixture are thus introduced directly at the heart of the mixing and turbulence area and vigorously ejected with the mixture circulating in the vat. Such a system makes it possible to ensure effective, homogenous mixing with a high flow rate (reduced introduction time and mixing time).
It has, however, appeared that such a system could also have certain limitations. It may in particular be desirable to further improve the introduction of the powder and to avoid any plugging and wetting of the introduction valve.